1. Field of the Invention
The present invention relates to a sheet feeder for feeding stacked sheets of paper one by one, and to a printer fitted with such a feeder.
2. Description of the Related Art
In some conventional sheet feeders, sheets of paper of various widths can be set selectively. Such a sheet feeder, where different sheets of paper are used, includes two feed rollers positioned in accordance with the width of the sheets for the most frequent use, which may be the sheets of the A4 size. An envelope for sheets of the A4 size is larger than them. When this envelope is placed in a sheet feeder with two feed rollers positioned for the A4 size, part of the envelope protrudes outside one of the rollers. In general, in order to separate one by one the envelopes or the sheets with some rigidity which are stacked in a sheet feeder, the top envelope or sheet is curved over a slope. When the envelope part outside the roller crosses the slope, this part makes high resistance against a surface of the sheet feeder, which may incline the envelope being fed with respect to a feeding direction. An envelope is made of a folded or doubled, relatively rigid sheet of paper. If one or both of the right and left edges of an envelope are bent or warped toward the surface of the sheet feeder, they are more rigid and make higher resistance.
A sheet feeder of a certain type includes a right sheet guide and a left sheet guide, which are interlocked with feed rollers. The rollers shift when the guides are shifted in accordance with the sheet width. In this case, also, the right and left edges of the sheets cannot be prevented from making resistance to the surface of the sheet feeder. Since this type of feeder needs a complicated mechanism for shifting the rollers and the guides depending on the sheet width, it is costly for manufacturing.
A sheet feeder of other type has more than four or five feed rollers provided coaxially on a common axis in order to conform to various size of sheet. This type of feeder also needs many components and much production cost.